Current implanted electrostimulation systems typically include a large impulse generator including a titanium case enclosing the power source and circuitry used to generate the electrical pulses. Due to the large size of these devices, the device itself is typically implanted within a cavity in the body such as under the clavicle, below the rib cage, in the lower abdominal region, or in the upper buttock. Electrical pulses are then delivered to a targeted nerve or muscle region via leads routed underneath the skin. Problems associated with this current approach include pocket infections, lead dislodgment, lead fracture or perforation, muscle tear due to implanting in or pulling out the leads, and limited locations for the placement of the electrodes.
The vast majority of wirelessly powered implantable devices operate in the strongly coupled regime, e.g., inductive coupling. In conventional wireless approaches using inductive coupling, the evanescent components outside tissue (near the source) remain evanescent inside tissue which does not allow for effective depth penetration of the wireless energy. Rectification techniques utilized for inductive coupling devices results in highly inefficient power conversion. For example, the rectification efficiency can be as low as 5% using these techniques.
Many conventional implantable devices use a backscattered (BS) technique for data transmission due to its simplicity in implementation. However, this technique can be very sensitive to the heterogeneous nature of the tissue medium and the data rate is limited. Furthermore, the data transmission performance can decay when implantable devices are placed deep in the tissue. To solve this problem, an active transmitter may be implemented but may consume substantial amount of power due to complexity in implementation.